Preparation of stable distillate fuels from cracked stocks



Patented Jan. 20, 1953 PRE ARATION F LE DIS A FUELS FROM cRAc sn crooksRussell H. Brown, Hammond, Ind., assignor to Standard Oil Company,Chicago, 111., a corporation of Indiana No Drawing. Application December19, 1949,

' Serial No. 133,905

8 Claims. 1 This invention relates to the preparation of stabledistillate fuels such as furnace oils, diesel oils, heater oils and thelike from cracked hydrocarbon stocks such as light gas oils produced bythermal cracking or particularly by catalytic cracking of high sulfurgas oils and/or reduced crudes. The term stable refers to stabilityagainst color, gum and sediment formation.

Heretofore it has been the practice to acid treat cracked (cycle) gasoil stocks of the distillate fuel boiling range, then percolate the acidtreated stock through clay and finally rerun the clayed stock. An objectof my invention is to avoid the necessity of acid treating and toprovide a simpler and less expensive method of preparing stabledistillate'fuel from cracked stocks. A further object is to provide amethod which will produce valuable byproduct materials. A further objectis to provide a stabilized distillate fuel from a cycle gas oil, Whichfuel may be blended with other distillate fuel components withoutadversely affecting the stability of the total blend; Other objects willbe apparent as the detailed description of the invention proceeds.

. The charging stock for my process is preferably a light catalyticcycle gas oil boiling in the range of about 400 to 750 F. and producedby the cracking of a high sulfur gas oil or reduced crude withconventional'solid siliceous cracking catalyst of the type described forexample in'Petroleum Processing, January 1947, page 5, et seq. Thecracking may be effected in fixed bed (Houdry or Cycloversion), movingbed (Thermof-or Catalytic Cracking), or powdered (Fluid) systems, theusual cracking temperature being in the range of about 800 to about1000* F. and the usual cracking catalysts being natural or syntheticsiliceous contact materials as exemplified by so. -cal1ed naturalcatalyst (acid treated montmorillonite), synthetic silica-alumina,silica-magnesia, silica-alumina-magnesia, etc., either with or withoutadditional components known to those skilled in the art. The light cyclegas oil which I employ as a charging stock is thatportion of the liquidproducts of catalytic cracking which boils above the gasoline boilingrange, but which is freed from components which are too high boiling foruse in distillate fuels. T e n en ion i 531 ifia i iebl 120 th r 2spending light cycle gas oil fraction produced by thermal cracking butit should be understood that stocks produced by thermal cracking are notequivalent to those produced by catalytic cracking and cracked stocksgenerally are very different from virgin stocks with respect tostability against color, gum and sediment formation. Treating processeswhich are adequate for virgin stocks are in most cases inadequate forcracked stocks because of the very different nature of the components inthe respective stocks which cause the formation of color, gum andsediment. The problem of stabilizing distillate fuels is also radicallydifferent from that of stabilizing cracked gasoline, and I have foundthat conventional anti-oxidants, such as aminophenols, have no utilityin the stabilization of distillate fuels and in some instances merelyaggravate the problem.

Caustic washing is a known refinery procedure for the treatment ofcracked stocks, but as ordinarily employed it does not convert a lightcycle gas oil into a stable distillate fuel. Among a vast'number ofadditives tested for the purpose, I have found that the most effectiveis a hydroxybenzaldehyde diimine exemplified by the formula HO A-CHN-R-N=CHAOH wherein A represents an aromatic group of the benzeneseries, the OH radical being attached directly to a ring carbon atompreferably ortho to the -CH= ,N group and R represents a hydrocarbonradical having the two N atoms attached directly to different carbonatoms thereof. While advantageous result 'm'ay be obtained where R is anaromatic group, a cyclo-aliphatic group or a 'heterocyclic groupcontaining nitrogen, the R is preferably an aliphatic radical of two tofive carbon atoms. For best results, particularly with respect toavoidance of sediment formation, a neutralized hydrocarbon phosphorussulfide reaction product, as described in U. S. 2,316,087, preferably aneutralized polybutene phosphorus sulfide reaction product as describedmore specifically in U. S. 2,316,080, should be used along with thehydroxybenzaldehyde diimine additive, each of the additives beingemployed in an amount in the approximate range of about 0.01 to 0.001weight per cent. a When this dual addiv s mp oyed i raw light cycle gasoil, it ef- 'fects some improvement in' color stability, but in manyca-sesiit' leads to even greater gum formation than would otherwise beencountered. However, when the dual additive is employed after the lightcycle gas oil has received a caustic wash, the stability against color,gum and deposit formation is improved to a far greater extent than wouldbe predicted from either treatment alone and the distillate fuel thusproduced by caustic washing followed by addition of dual additive can beblended with other distillate fuel stocks to meet stringent distillatefuel specifications.

The caustic wash of the light cycle gas oil should be eifected on thelight cycle gas oil stream as it leaves the fractionators in thecracking system, i. e. without intermediate storage or exposure to theatmosphere. The concentration of the caustic solution is not criticaland while very good results have been obtained with caustic solutions asdilute as 5 weight per cent, it is preferred to employ a solution ofabout 25 weight per cent. Ordinary temperatures and atmosphericpressures may be employed provided that the desired intimacy of contactis obtained, but for large scale operation it is preferred to introducethe light cycle gas oil into the caustic wash system before it is cooledvery much below about 150 F., the caustic wash usually being effected inthe range of about 75 to 150 F. The amount of caustic required will ofcourse be somewhat dependent upon the amount of sulfur compounds to beremoved, but with a charging stock containing about .2 per cent byweight of thiophenols, about 45 barrels per day of 25 per cent causticis sufficient to treat 10,000 barrels per day of charging stock. Thecaustic solution is most effective when it contains a small amount ofdissolved caustic cresylate, but its effectiveness is radicallydiminished if it becomes loaded with too much neutralized cresols orthiocresols. Thus when successive one liter portions of light catalyticcycle stock were shaken for five minutes with the same 20 cc. of 25percent NaOH solution, and then with 500 cc. of water for one minute,the following data were obtained before and after adding the dualinhibitor (which in this case was 0.001% of the neutralized'polybutenephosphorus sulfide reaction product and 0.001% of N:N disalicylidene 1:2diaminoprop-ane) Inhibited with v No Inhibitor 0.001% SA-26,

Caustic Used 001% GD'452 O.D. Gum O. D. Gum

None 75.0 20. 2 48. 5 34. 2

Fresh Caustic 17. 7. 7 l3. 6. 6

Once Used Caustic 19. 0 8. 4 14.0 5.0

Twice Used Caustic 18. 6 6. 4 l4. 5 4. 3

3 Times Used Caustic- 25.5 7. 8 l5. 7 5.2

4 Times Used Oaustic 30. 5 l0. 0 l9. 7 6. 7

5 Times Used Caustic.-- 47. 5 23.8 27. 0 10. 4

6 Times Used Oaustic 41. 5 21. 5 32. 5 l5. 7

X Optical density of 5 cc. of sample heated for hours at 200 F. anddiluted with 20 cc. of xylene.

2 Gum in mg./l00 cc. by acid 1100 method after 20 hours at 200 F.

The above data show that twice, used caustic is even more eifective thanfresh caustic with respect to gum formation, both in the presence andabsence of inhibitor or additive. It shows that in the absence ofcaustic washing, the addition of dual inhibitor resulted in more gumformation than in the uninhibited charging stock before caustic washing.It shows that the five and six times used caustic resulted (in theabsence of inhibitor) in a product of higher gum content than in theoriginal charging stock.

The intimate mixing of the caustic with th charging stock can beobtained by ordinary agitation, such as shaking (as employed inlaboratory technique) or by passing charging stock upwardly through acaustic solution in a tower which is preferably packed with Raschigrings or other known packing material for increasing contact (as I havedemonstrated in pilot plant operations) or it may be effected by simplypassing charging stock and aqueous caustic solution through a bafilechamber-or knot hole mixer; in other words, any known mixing means maybe employed.

In a particular 10,000 barrel per day plant, the charging stock, atabout 150 F. and p. s. i. g.. is mixed with a caustic solution streamwhich is circulated at the rate of 2500 barrels per day, the mixturebeing settled in a horizontal vessel about 10 feet in diameterand 30feet long at a pressure of about 72 p. s. i. g. with most of the settledcaustic being recirculated, but about 70 barrels per day of spentcaustic being withdrawn and about 45 barrels per day of 25 weight percent NaOH (specific gravity 1.277) being introduced as make-up. Valuablec'resols and thiocresols may, of course, be recovered from the spentcaustic by procedures known to those skilled in the art.

After the caustic wash treatment, the charging stock is washed with alarge volume of water and the wash water separated therefrom. In mallscale operations, the wash Water may simply be agitated with the causticwashed charging stock and the mixture allowed to settle, a filter or acoalescer preferably being employed to facilitate a clean separation ofwashwater from treated oil. In the 10,000 barrel per day planthereinabove referred to, the caustic washed charging stock from the topof the settling drum is admixed with wash water at the rate of 2500barrels per day, passed through a mixer for obtaining thorough andintimate contact, and then allowed to settle in a water wash drum aboutthe same size as the caustic wash drum. The settled wash water iswithdrawn to the sewer and the washed oil is preferably passed upwardlythrough a salt drum for coalescing and removing any residual water.Other known coalescing or drying means may, of course, be used insteadof the salt drum. Entrained water (or brine in the case of the'saltdrum) is withdrawn from the base of the coalescer tower.

As dry, washed charging stock is passed to passed to storage, th dualinhibitor materials are added thereto by means of p'roportioning pumps.In the commercial plant, where washed material is passed to storage atthe rate of approximately 10,000 barrels per day, a duplex proportioningpump introduces into this stream N,N disalicylidene-1,2-diaminopropaneas an 80 weight per cent solution in xylene at the rate of 1.44 pintsper hour, and neutralized polybutene phosphorus sulfide reaction productas a 60 weight per cent solution in a light lubricating oil of SAE-lOgrade at the rate of 2.15 pints per hour. The resulting caustic Washedproduct containing the dual additive is very stable against color, gumand sediment formation and may be blended with other distillate fuelblending stocks to meet required distillate fuel specifications.

In the above example, the caustic consumption is about .5 pound ofNaOI-I per barrel of light cycle gas oil, but as hereinabove stated,this amount is based on'a particular charging stock and the amount ofrequired caustic will naturally .5 depend upon the nature of the chargStock and the color specifications to be met. Potassium hydroxide may beused instead of sodium hydroxide, but I have found that sodiumcarbonate, sodium bicarbonate, and ammonium hydroxide are not effectivefor use in my process of stabilizing light catalytic cycle stock.Treatment of the oil with a suspension of calcium oxide in water gavesome increase in the stability of the oil, but is not as desirable asthe alkali metal hydroxides. Even the treatment with aqueous alkalimetal hydroxides per se was not effective for obtaining the requiredtested fuel stability.

A vast number of additives were tested for their effectiveness instabilizing distillate fuel prepared from light cycle gas oil and it wasfound that most of the additives, particularly those employed asanti-oxidants and stabilizers in cracked naphtha, were ineffective forstabilizing either the'raw or caustic washed light cycle gas oil. Theoutstanding additive or inhibitor was N:N disalicylidene 1:2diamino-propane, which may be represented by the formula where A is abenzene ring and R. is an aliphatic three carbon atom radical.Equivalent results are obtainable where R is a two carbon atom radical,four carbon atom radical, or five carbon atom radical with the carbonatoms in either straight or branched position. Other compounds of thiseneral type are described in considerable detail in U. S. 2,282,513wherein they are described as color inhibitors for lubricating oils,particularly in the presence of metal. In my case, the light cycle gasoil is not a lubricating oil, it does not follow an acid treatment andapparently it does not function as a metal deactivator. functions as athiocresol deactivator, but of course the exact mechanism by which theaddit'ive functions in my process is'not known. The simple fact is thatthe material in my process is employed in caustic Washed light cycle gasoil which is very different from the cracked gasoline of U. s. 2,181,122or th lubricating oil of U. S. 2,282,513. No copper or other metalcontaminant is present in my light cycle gas oil and no anti-oxidant isemployed which would require the presence of a copper deactivator forprotection. In other words, I have discovered that the type of compoundsreferred to in U. S. 2,181,122 and U. S. 2,282,513 as copperdeactivating compounds may be employed to serve an entirely differentfunction, namely that of stabilizing a caustic washed light cycle gasoil against the formation of gum and sediment as well as color,particularly when it is employed in conjunction with the neutralizedpolybutene phosphorus sulfide reaction product.

For some light cycle gas oil charging stocks, particularly when they areto be stored for relatively short periods, the caustic wash followed bywater wash and addition of the additive is effective in the absence ofthe neutralized hydrocarbon phosphorus sulfide reaction productadditive. The following results are typical of data obtained inaccelerated tests wherein the light cycle gas oil samples weremaintained for 20 hours at a temperature of 200 F., the single additivebeing N,N-disalicylidene-1,2- diaminopropane in amounts of .001 to .01percent It appears more likely that the additive e 6 by weight, the termgum meaning the amount of gum in milligrams per 100 cc. by the acid 1100method.

The above data show that caustic. wash followed by water washing and theuse of the single additive is vastly superior to acid treating followedby clay percolation, which in similar accelerated tests of 20 hours at200 F. gave products of about 3.5-4 NPA color and about '10-15milligrams of gum per 100 cc.

The following data are typical of those obtained in accelerated testswherein the light cycle gas oil samples were maintained for 20 hours ata temperature of 200 F., the expression dual ad-' ditives referring toboth N,N-disalicylidene- 1,2-diaminopropane and neutralized polybutenephosphorus sulfide reaction product, each employed in amounts of about.001 to .01 weight per cent, the term 0. D. in this case referring tooptical density of cc. of sample diluted with cc. of xylene (anindication of color) SAMELE D Caustic Dual Ad- NBA Wash ditives ColorGum 0 No No 3% 19.9 58.0 No Yes 11 16. 8 l6. 5 Yes No 1% 12. 7 17.0 YesYes 0-1 9. 0 12.0

SAMPLE E N0 N0 4V 29. 1 6-1.0 No Yes my? 31.7 24.5 Yes No 2-2k 10. 7'22. 5 Yes it es v1-1/ 6. 0 14. 0

SAMPLE F N0 N0 4% 20.2 75.0 No Yes 3% 34. 2 48. 5 Yes No 1.1% 7. 7- 17.0Yes Yes 111% 6. 6 l3. 5

Accelerated tests cannot always be relied upon to give a true measure ofstability over-along period of time, particularly with regard tosediment formation. Usually no sediment occurs in storage for as much astwo or three months at 90 F., but in the absence of the treatment hereindescribed, sediment becomes appreciable at six months and even greaterafter a year's storage. The following data are illustrative of resultsobtained in twelve month storage tests at;90""F., 'the sedimentformation being reported in more or less arbitrary units of the testemployed.

SAMPLE G Caustic Dual NPA Gum Sedi- Wash Additives Color ment No No 3.522.7 4 No Yes 2 13.8 3 Yes No 2 17.4 none Yes Yes 1. 5 5. 1 none SAMPLEH No No 2.5 27.7 4 No Yes 3 22.5 4 Yes No 2 22.2 1 Yes Yes 1. 5 12. 7none n3 Neutralized butene polymer phosphorus sulfide reaction producty.

Samples A to H were all on light catalytic cycle gas oil. Light thermalcycle gas oil (produced by thermal cracking instead of catalyticcracking) may also be stabilized against color, gum and sedimentformation by my caustic wash followed by water wash and addition of theHOA-CH=NR-N=CHAOH additive. The following data show results obtained inthe accelerated tests (20 hours at 200 F.) as applied to thermal cyclegas oil, the additive in this case being .001 per cent by weight of N,N-disalicylidene-1,2-diamin0propane:

SAMPLE I Caustic Single NPA Wash Additive Color Gum No No 6 30. 9 No Yes4 26. Yes No 3.5 16. 6 Yes Yes 2. 5 7. 0

A years storage test at 90 F. with thermal cycle gas oil employing dualadditive (as with Samples D to H) gave the following results:

SAMPLE I Caustic Dual NPA Gum Sedi- Wash Additives Color ment No No 525.4 3 No Yes 3 23. 3 1 Yes Yes 2 8.2 none While it might have beenpredicted from the testings of U. S. 2,282,513 that the additivecomponent described therein would improve color stability, it will benoted that the additive used on raw cycle catalytic gas oil did notstabilize color to the desired extent and in some cases (Samples B, Eand F) actually increased the amount of gum which was formed. Thecaustic wash per se was ineifective for obtaining the desired stabilityagainst color, gum and sediment formation. However, the combined use ofthe preliminary caustic wash (followed by water wash) and additiveresulted in the production from light cycle gas oils of distillate fuelblending stocks characterized by a remarkably good color and aremarkable stability not only against color formation, but also againstgum and sediment formation.

The stabilized distillate fuel products of my inventionmay be blendedwith distillate fuel stocks 7 produced from virgin gas oils to producean ultimate product of higher burning quality index, i. e. an ultimateproduct which has less tendency to form burner deposits. The followingdata show the eflect of treating a light catalytic cycle gas oil inaccordance with my invention when the treated product is blended with anequal volume of a virgin gas oil, these tests having been made underaccelerated test conditions (20 hours at 200 F.), the expressionuntreated meaning raw cycle gas oil, and the expression treated meaningcaustic washed, water washed and inhibited with 0.001 per cent ofN,N-disalicylidene-1,2- diaminopropane plus 0.001 per cent ofneutralized polybutene phosphorus sulfide reaction product.

SAMPLE K Cycle Gas Oil Virgin Gas Oil NPA.

Component Component Color Gum seamen:

Untreated Mid-Continent 3%4 14.4 Yes Treated ...do l-B 5. 3 No UntreatedWest Texas 3 14.0 Yes 'lreated d0 1% 5. 4 No It should be understood, ofcourse, that the cycle gas oil which has been treated in accordance withmy invention may be blended with distillate fuel blending stocks otherthan virgin gas oils and that in all cases, the treatment of the cyclegas oils improves the stability of the final blend.

As hereinabove stated, beneficial results are attainable with the singlepercent of a neutralized polybutene phosphorusv sulfide reaction productand about 0.01 to 0.001 weight per cent ofN,N'-disalicylidene-1,2-diaminopropane.

2. A stabilized distillate fuel blending stock which consistsessentially of a cracked hydrocarbon oil boiling in the range of about400 F. to 750 F. which has been washed with an aqueous alkali metalhydroxide solution and then freed from aqueous caustic solution andwhich contains about 0.01 to 0.001 weight per cent of a neutralizedpolybutene phosphorus sulfide reaction product and about 0.01 to 0.001weight per cent of N,N'-disalicylidene-1,2-diaminopropane.

3. The method of stabilizing a cracked light hydrocarbon distillatewhich is higher boiling than gasoline and of substantially the heateroil boiling range, which method comprises intimately contacting saiddistillate with an aqueous alkali metal hydroxide solution at atemperature in the range of about 75 to F., freeing the contacteddistillate from aqueous caustic solution, then coalescing and removingresidual water from the distillate, and finally incorporating in saiddistillate about .01 to .001 weight per cent of a neutralized polybutenephosphorus sulfide reaction product and about .01 to .001 weight percent of N,N'-disalicylidene-1,2-diaminopropane.

4. The method of treating a cracked hydrocarbon oil boiling chiefly inthe range of 400 F. to 750 R, which method comprises washing said oilwith an aqueous alkali metal hydroxide solution at a temperature in therange of about 75 F. to 150 F., freeing the washed oil from aqueousalkali metal hydroxide solution and then incorporating in said washedoil an amount in the range of about .01 to .001 weight percent of ahydroxybenzaldehyde diimine having the formula HOA--CH=NRN=CHAOH whereinA represents an aromatic group of the benzene series, the OH radicalbeing attached directly to a ring carbon atom ortho to the CH=N group,and R is an aliphatic hydrocarbon radical having 2 to 5 carbon atoms andhaving different carbon atoms thereof attached directly to the two Natoms.

5. The method of claim 4 wherein the hydroxybenzaldehyde diimine isN,N'-disalicylidene-1,2- diamopropane.

6. The method of claim 4 which includes the step of also incorporatingin said Washed oil an amount in the range of about .01 to .001 weightpercent of a neutralized polybutene phosphorus sulfide reaction product.

7. A stabilized distillate fuel which consists essentially of a crackedhydrocarbon oil boiling chiefly in the range of 400 F. to 750 F. whichhas been washed with an alkali metal hydroxide solution and then freedfrom said solution and 10 which contains an amount in the range of about.01 to .001 weight percent of a hydroxybenzaldehyde diimine having theformula REFERENCES CITED The following references are of record in thefile of this patent:

UNITED STATES PATENTS Number Name Date 2,150,084 Tannehill Mar. 7, 19392,181,122 Downing et a1. Nov. 28, 1939 2,267,109 Kendall Dec. 23, 19412,282,513 Downing et a1. May 12, 1942 2,316,080 Loane et a1 Apr. 6, 19432,316,087 Gaynor et a1. Apr. 6, 1943

1. THE METHOD OF TREATING CRACKED HYDROCARBON OIL BOILING IN THE RANGEOF ABOUT 400* F. TO 750* F. WHICH COMPRISES WASHING IT WITH AN AQUEOUSSOLUTION OF AN ALKALI METAL HYDROXIDE, SUBSEQUENTLY REMOVING SAIDSOLUTION FROM IT AND SUBSEQUENTLY ADDING TO IT ABOUT 0.01 TO 0.001WEIGHT PER CENT OF A NEUTRALIZED POLYBUTENE PHOSPHORUS SULFIDE REACTIONPRODUCT AND ABOUT 0.01 TO 0.001 WEIGHT PER CENT OFN,N''-DISALICYLIDENE-1,2-DIAMINOPROPANE.